Dissimilar compositions for electrical contact pairs



United States Patent 3,532,844 DISSIMILAR COMPOSITIONS FOR ELECTRICAL CONTACT PAIRS Childress B. Gwyn, Jr., Wethersfield, Conn., assignor to Talon, Inc, Meadville, Pa., a corporation of Penn- 3,532,844 Patented Oct. 6, 1970 and to 20% by Weight of cadmium, while at least the contacting surface of the cooperating contact is formed of 80 to 95% by weight of silver and 5 to 20% by weight of cadmium oxide. The contacts can be produced in any desired manner well known to those skilled in the art, and

sylvania 5 could take any desired form such as rivets, clad surfaces, No Drawing. Filed Oct. 26, 1967, Ser. No. 678,206 and the like.

Int- Cl- H01h 1/ It is, therefore, a primary object of this invention to de- 5 Clalms crease mechanical and electrical wear of cooperating con- I tacts.

Another object of this invention is to decrease the re- ABSTRACT OF THE DISCLOSURE sistance rise of a pair of cooperating contacts. Two cooperating contacts are formed of silver cadmium A further object of this invention is to decrease the posand silver cadmium oxide alloys, respectively, where the sibility of welding in a pair of cooperating contacts. silver cadmium contact is from 80 to 95 by weight silver These and other objects of this invention will become and 5 to by weight cadmium, while the other contact more apparent from the following examples: is from 80 to 95% by weight silver and 5 to 20% by A number of 4 inch diameter contacts were made of weight cadmium oxide. different compositions by standard techniques. The contacts were then arranged in a standard relay actuated by a 20 magnet coil with a uniform contact pressure of 30 ounces. This invention relates to electrical contacts, and more The contacts were then connected in a 220-volt 60-cycle particularly relates to the use of dissimilar materials for line with a motor load (to form an inductive circuit), and cooperating contacts. the current at contact separation was measured by obser- The use of the same material for cooperating contacts vation in an oscilloscope and is shown in the following is well known, and silver cadmium alloys of the same comchart.

Approx. percentf 0 Approx. electrical Peak power Total and/or Contact current, Type of factor, number of mechanical IHD amps loading percent operations wear 140 Motor.-. 65 58 151 do 65 2 1, 222 34 1 425 23 146 do 65 2 6,000 140 do 65 g 12 153 do 65 g gg 12 151 do 65 2 14 1 Before welding. 2 Before final failure.

position for cooperating contacts, or the use of silver cadmium oxide of the same composition for cooperating contacts is old and well known. It is also known that cooperatingcontacts of different composition can sometimes create improved contact service as shown, for example, in U.'S. Pats. 2,300,286, 2,815,421, or 3,128,540.

In accordance with the present invention, it has been discovered that the use of silver cadmium for one of a pair of contacts, and silver cadmium oxide for the other of the pair of contacts provides unexpected and substantial improvements in the contact efiiciency in regards to contact resistance, contact life, and contact arcing properties. More particularly, at least the contacting surface of one of the In the above chart, the first three pairs of contact materials were of conventionally similar contact material.

The second three groups tested were, in accordance with the invention, selected of one contact of silver cadmium and the other of silver cadmium oxide. These last three pairs of materials, as shown, exhibit a dramatic improvement in number of operations to initial welding (or sticking) and to final failure (or complete welding). The consequent electrical and mechanical wear of the contact surfaces was decreased by more than 100% The test described above was then repeated in a resistance circuit, using a tungsten lamp load in place of the motor, using fresh contact elements. The following chart contacts is formed of from to by Weight of silver 55 gives the result of this resistive test.

Approx Total percent number of of electrical Peak operations, and/or Contact current, Type of Power before mechanical combinations amps loading factor welding erosion 300 Tungsten lamps....- 1. 0 z' 'gfi 38 300 do 1.0 2% do 1.0 g' 34 108 .do 1.0 16 303 do 1.0} 11 298 do 1.0

Initial. 9 Final failure.

Again, it will be seen that the solution dissimilar materials for the contacts, in accordance with the invention, provides substantial improvement in the contact operation and life.

Although this invention has been described with respect to its preferred embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in the art, and it is preferred, therefore, that the scope of the invention be limited not by the specific disclosure herein, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. In combination, a pair of cooperable contacts movable into and out of engagement with respect to one another; one of said contacts having a contacting surface composed of a silver-cadmium alloy; the other of said contacts having a contacting surface composed of a silver cadmium oxide alloy; and the two contacts together providing greatly reduced susceptibility to sticking and Welding, and to electrical and mechanical wear, than provided by many contact combinations of similar and other dissimilar compositions.

2. The combination of claim 1 wherein said silver cad- 4 mium alloy is composed of from 80 to 95% by weight silver and of from 5 to by weight of cadmium.

3. The combination of claim 1 wherein said silver cadmium oxide alloy is composed of from to 95% by weight silver and of from 5 to 20% by weight cadmium oxide.

4. The combination of claim 2 wherein said silver cadmium oxide alloy is composed of from 80 to 95% by weight silver and of from 5 to 20% by weight cadmium oxide.

5. The combination of claim 1 wherein said silver cadmium alloy is composed of about by weight of silver and 15% by weight of cadmium and wherein said silver cadmium oxide alloy is composed of 85% by weight of silver and 15% by weight of cadmium oxide.

References Cited UNITED STATES PATENTS 2,675,445 4/1954 Youhouse. 2,861,155 11/1958 Farnham et al.

HERMAN O. JONES, Primary Examiner 

